Set SOFT_INPUT_STATE_ALWAYS_HIDDEN for ImeEditorPopupDialogActivity

In CloseImeEditorPopupDialogTest#imeLayerAndImeSnapshotVisibleOnScreen
that we are mainly verifying the IME snapshot animation will visible as
expected and not expect IME visible after dismissing the editor popup
dialog to back to the main window.

In case IME may visible on top of the
main window by the fallback input connection to cause the IME flicker,

set SOFT_INPUT_STATE_ALWAYS_HIDDEN on the main activity to ensure IME
window will end up hidden as expected.

Fix: 240587808
Test: atest FlickerTests#CloseImeEditorPopupDialogTest \
        --rerun-until-failure 10
Change-Id: I569feb7b8f8bb50abd69d09eb982e362d74515fe